Radiographic intensifying screen



Jan. 11, 1955 H. F. MESICK, JR 2,698,991

RADIOGRAPl-IIC INTENSIFYING SCREEN Filed Nov. 15, 1950 METALLIC SHEET in GLASS CLOTH IMPREGNATEO WITH ALKYD RESIN Inventor Harms PMesichJrgDeceased, Edith M. Mesick, Administratrix,

Afitor'hey.

United States Patent RADIOGRAPHIC INTENSIFYING SCREEN Harry F. Mesick, Jr., deceased, late of Schenectady, N. Y., by Edith M. Mesick, administratrix, Cableskill, N. Y., assignor to General Electric Company, a corporation of New York Application November 15, 1950, Serial No. 195,741

4 Claims. (Cl. 29-195) This invention relates to radiography and, more particularly, to fabrication of intensifying screens employed in radiographic apparatus.

In the past few years, the use of lead intensifying screens in high voltage radiography has become standard practice in most radiographic laboratories. A piece of unexposed photographic film is placed between a pair of lead intensifying screens before being exposed to high voltage X-ray radiation. With the use of intensifying screens, the density of the emulsion remaining on the film after it has been exposed and developed is much greater than with the use of photographic film alone. Many methods of handling and fabricating thin lead intensifying screens have been developed, but, as a rule, none of these methods are particularly satisfactory. Cassettes, which are rigid frames for holding the intensifying screens and the unexposed film during exposure to X-ray radiation, are used in much radiographic apparatus to assist in providing a uniform contact between the intensifying screens and the film. Because the thickness of the lead intensifying screen is only a few mils, a backing for the screens is desirable to facilitate handling, especially since the film and intensifying screens must generally be removed from a cassette in darkness and the backing of the screen should be as thin as possible to reduce the amount of X-ray absorption in the backing material. Backing of the thin lead screens by means of rubber or plastic has been employed, but because this provides an extremely flexible screen, the films are easily bent when handled. To prevent this bending, a thick backing is often used, but this limits the efiectiveness of the screen by increasing the X-ray absorption of the backing.

In industry, both flat or plane radiographs and curved radiographs are common. In the radiographing of castings, for example, the film is sometimes curved such that it conforms to the shape of the particular object being photographed and, in such a case, it is, of course, still necessary that a uniform contact between the screens and the film be provided over the entire surface of the film. Presently, separate intensifying screens are used for these different purposes, but it is, of course, desirable that a universal type screen be developed.

An object of the invention is to provide a new and improved backing for thin lead intensifying screens.

Another object of the invention is to provide a thin lead intensifying screen having a suitable backing which has a low X-ray absorption factor.

Another object of the invention is to provide a backing for thin lead intensifying screens which facilitates handling of the screens with a minimum possibility of bending.

Another object of the invention is to provide a lead intensifying screen having a backing such that the screen is suitable for both plane and curved applications.

In the attainment of the foregoing objects, there is provided a backing of glass cloth which is impregnated with a polymerizable unsaturated alkyd resin to which is bonded the intensifying sheet of lead. This backing, which has a thickness of the order of mils, provides a screen which has enough flexibility such that it may be curved to conform to the shape of irregular members being radiographed, and yet has a high enough elastic limit such that when the irregular pressure is removed from the screen it will return to its original plane shape. This intensifying screen may be handled with facility 2,698,991 Patented Jan. .11, 1955 with a minimum possibility of bending and, hence, with a minimum possibility of destroying the usefulness of the screen.

For additional objects and advantages, and for a better understanding of the invention, attention is now directed to the following description and accompanying drawing and also to the appended claims in which the features of the invention believed to be novel are particularly pointed out.

Referring to the drawing, a backing 1 of thin glass cloth which is impregnated with a resin is laminated with a thin metallic sheet 2. It is known in the art that a successful intensifying screen should consist, in part, of a thin metallic layer whose atomic weight is relatively high; therefore, lead, which is relatively inexpensive as compared to the cost of other high atomic weight materials, is generally used for such screens.

The resin with which the glass cloth is impregnated is a solution of a mixture of an unsaturated alkyd resin, a polyallyl ester of a polycarboxylic acid, a polyvinyl acetal, and a cure accelerator, e. g., benzoyl peroxide,

such resinous compositions being more particularly disclosed and claimed in Loritsch Patent 2,526,239, and assigned to the same assignee as the present invention. The unsaturated alkyd resin is the reaction product of a polyhydric alcohol and an unsaturated polyoasic acid. For example, it is preferred to use diethylene glycol maleate resin for the unsaturated alkyd resin, diallyl phthalate for the polyallyl ester of a polycarboxylic acid, and for the polyvinyl acetal a polyvinyl formal resin obtained by the reaction of formaldehyde and a partially hydrolyzed polyvinyl acetate, the entire resinous mixture being dissolved in a solvent comprising, for instance, toluene and ethyl alcohol.

Metallic sheet 2 is pressed to backing 1 under a pressure of approximately 300 pounds per sq. in. and held at a temperature from about C. to C. for 15 minutes to bond the glass and metal layers together with the resin at the same time it is cured. After removal of the pressure, the fabricated screen may be further cured at a temperature greater than 100 C. for approximately 24 hours, after which time the intensifying screen is ready for use. lt will be apparent that this same fabrication may be made by coating one side of a piece of glass cloth with the resinous solution, laying the metallic sheet upon this coat, and compressing the combination with heat so that the resinous solution impregnates the glass cloth, bonds the glass cloth to the metallic sheet and cures all in the same operation.

Lead intensifying screens ranging in lead thickness from S to 40 mils using an impregnated glass cloth backing having a thickness of approximately 10 mils permit the application to the front surface of the lead of a very thin layer of another suitable'high atomic weight material such, for example, as gold or platinum. A screen of this type, having a gold-plated layer of approximately one-tenth of a mil on a lead screen, is not as easily oxidized and scratched as is a lead surface screen.

An intensifying screen of this type, with or without the gold plate, having an impregnated glass cloth backing will withstand a considerable amount of flexing and continued use without physical damage. This type of screen, by virtue of the stable backing, permits various methods of cleaning which are not possible with other prevailing screen assemblies. Some suitable cleaners are acids, weak alkali, and solvents. This screen is also able to withstand appreciably high temperatures without losing any of its desirable characteristics, which are flexibility, high elastic limit, and low X-ray absorption by the backing material.

While this invention has been disclosed with respect to a particular application, it is understood that those skilled in the art may make many modifications, and, therefore, by the appended claims it is intended to cover any such modifications which may fall within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is: v:

l. A planar intensifying screen for use in radiographic. apparatus, comprising a lead foil sheet and a glasscloth adhered thereto, said cloth being impregnated with and bonded to said sheet by a composition comprising a polymerizable unsaturated alkyd resin, said screen being of such thickness and flexibility as to restore itself to planar form after flexing.

2. A planar intensifying screen for use in'radiographic apparatus, comprising a lead foil sheet having a thin layer of gold plating on one side and a glass cloth ad'- hered to the other side, said cloth beingimpregnated with and bonded to said sheet by a composition comprising a polymerizable unsaturated alkydresin, said screen being of such thickness andflexibility as:to restore itself to planar form after flexing.

3. A planar intensifying screen for use in radiographic apparatus comprising a lead foilsheet and a glass cloth adhered thereto, said cloth being impregnatedwith and bonded to said sheet by a composition comprising a mixture of diethylene glycol maleate resin, diallyl phthalate, and a-polyvinyl formal resin obtained by the reaction of formaldehyde and a partially hydrolyzed polyvinyl acetate, said screen being of such thickness and flexibility as to restore itself to'planar form after flexing.

4. An intensifying screen-for use in radiographic apparatus, comprising a lead foil planarsheet of a-thickness of approximately 5 mils to approximately 40 mils, a

glass fabric backing for the sheet approximately 10 mils in thickness, and a composition comprising a polymerizable unsaturated alkyd resin adhesively securing said glass fabric to one surface of'said sheet and impregnating said fabric, whereby said screen has the property of self restoration to its original planar form after flexing.

References Citedin the fileof this patent UNITED STATES PATENTS OTHER REFERENCES Some- Experiments on Electrodeposition of Gold from Alkaline Cyanide Solutions by E. Dustan, published in Electrometallurgy (Supplement to-the Metal Industry) at page 295 (only), Mar; 13, 1931;

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